Parallax, or more accurately motion parallax (Greek: παραλλαγή (parallagé) = alteration) is the change of angular position of two stationary points relative to each other as seen by an observer, caused by the motion of an observer. Simply put, it is the apparent shift of an object against a background caused by a change in observer position.

You should be able to find a number of decent scopes for under 2 bills, such as the Nikon Prostaff, Burris Fullfield II and I believe you can even find a Bushnell 3200 Elite in certain places as well.